1. Field of the Invention
This invention pertains to improvements in controlled heat treating processes and apparatus. More particularly, this invention pertains to a fluidized bed heat treatment apparatus with submerged infrared radiation heating sources. The invention also pertains to a method of using such an apparatus for reclaiming foundry sand.
2. Description of the Prior Art
The use of fluidized bed furnaces for heat treating a product is well known. Such furnaces heat a bed of particles so as to develop an extremely hot bed of fluidizing particles such as, for example, aluminum oxide. The furnaces can be used for both the continuous processing of a product or the batch processing products.
U.S. Pat. No. 4,752,061 teaches a fluidized bed furnace which uses infrared radiation as the heating source. One advantage of using infrared radiation as the heating source is that it permits the use of inert gases fluidize the particles within the furnace. As a result, a controlled atmosphere can be provided surrounding the product being heat treated within the furnace.
The aforenoted U.S. Pat. No. 4,752,061 places the infrared lamps out of the bed behind a quartz wall or screen. As a result, the distance from the infrared lamps to the bed results in the development of a high temperature gradient within the bed with too little of the energy source contributing to the heating of the bed. This leads to a significant amount of energy inefficiency. In addition, the infrared lamps may be disposed in close proximity to the stainless steel retort. This could result in partial melting of the retort.